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cxl: docs/allocation/hugepages
Add docs on how CXL capacity interacts with CMA and HugeTLB allocation
interfaces.
Signed-off-by: Gregory Price <gourry@gourry.net>
Link: https://patch.msgid.link/20250512162134.3596150-17-gourry@gourry.net
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
authored by
Gregory Price
and committed by
Dave Jiang
df63e012
f109e77d
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Documentation/driver-api/cxl/allocation/hugepages.rst
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Documentation/driver-api/cxl/allocation/hugepages.rst
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.. SPDX-License-Identifier: GPL-2.0
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==========
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Huge Pages
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==========
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Contiguous Memory Allocator
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===========================
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CXL Memory onlined as SystemRAM during early boot is eligible for use by CMA,
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as the NUMA node hosting that capacity will be `Online` at the time CMA
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carves out contiguous capacity.
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CXL Memory deferred to the CXL Driver for configuration cannot have its
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capacity allocated by CMA - as the NUMA node hosting the capacity is `Offline`
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at :code:`__init` time - when CMA carves out contiguous capacity.
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HugeTLB
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=======
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Different huge page sizes allow different memory configurations.
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2MB Huge Pages
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--------------
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All CXL capacity regardless of configuration time or memory zone is eligible
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for use as 2MB huge pages.
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1GB Huge Pages
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--------------
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CXL capacity onlined in :code:`ZONE_NORMAL` is eligible for 1GB Gigantic Page
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allocation.
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CXL capacity onlined in :code:`ZONE_MOVABLE` is not eligible for 1GB Gigantic
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Page allocation.